Trim the leeks, halve them lengthways and finely slice. Rinse them thoroughly because they often have bits of soil between the layers.
Warm the olive oil in a large saucepan and fry the leeks and garlic gently for 10-15 minutes with the lid on, to soften without colouring.
Drain the chickpeas and add them to the pan with the vegetable stock.
Bring to the boil and simmer for 5 minutes.
Take about half the soup out of the pan and blend it carefully (it's hot!).
Return the blended soup to the unblended soup in the pan, stir well and bring back to the boil.
Serve with freshly ground black pepper.